EP3573208A1 - Circuit de commande de puissance et procédé de stabilisation d'une alimentation électrique - Google Patents

Circuit de commande de puissance et procédé de stabilisation d'une alimentation électrique Download PDF

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Publication number
EP3573208A1
EP3573208A1 EP19181726.1A EP19181726A EP3573208A1 EP 3573208 A1 EP3573208 A1 EP 3573208A1 EP 19181726 A EP19181726 A EP 19181726A EP 3573208 A1 EP3573208 A1 EP 3573208A1
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EP
European Patent Office
Prior art keywords
power
mains
load
control circuit
frequency
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP19181726.1A
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German (de)
English (en)
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EP3573208B1 (fr
Inventor
Shu Yuen Ron Hui
Chi Kwan Lee
Felix Fulih Wu
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Versitech Ltd
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City University of Hong Kong CityU
Versitech Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1807—Arrangements for adjusting, eliminating or compensating reactive power in networks using series compensators
    • H02J3/1814—Arrangements for adjusting, eliminating or compensating reactive power in networks using series compensators wherein al least one reactive element is actively controlled by a bridge converter, e.g. unified power flow controllers [UPFC]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
    • H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/10—Flexible AC transmission systems [FACTS]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/20—Active power filtering [APF]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

Definitions

  • the present invention relates to power control circuits and methods for stabilizing power supplies, and in particular, but not limited to, circuits and methods of this type that are used with distributed loads connected to a dynamically changing power supply, such as that generated by dynamically changing renewable energy sources.
  • reactive power controllers also known as reactive power compensators
  • reactive power controllers have been well-researched as a tool to provide voltage stability in power transmission lines as early as 1982, as shown in T.J. Miller, "Reactive Power Control in Electric Systems", John Wiley & Sons, 1982 .
  • the basic concept of using reactive power for voltage stability control can be illustrated in Fig.1a , in which the equivalent circuit and its vector diagram for an ac mains voltage and the transmission line impedance are shown. It can be seen from the vector diagram that the output voltage V 2 is reduced because of the transmission line resistance and impedance.
  • the active (which is also known as “real”) and reactive (which is also known as “imaginary”) source current are labelled as I P and I Q , respectively.
  • the active current I P is in phase with V 2 and will contribute to real power consumption in the load.
  • the reactive current I Q is 90° out of phase (lagging behind) V 2 and will not contribute to real power dissipation. Therefore, the power associated with I Q is called reactive power because it flows into and out of the system without being dissipated.
  • a reactive current (and its associated reactive power) is injected into the system as shown in Fig.1b , the voltage drop due to the reactive current I Q can be compensated by the injected current I Q '.
  • the output V 2 can be increased or boosted because its voltage drop can be reduced.
  • I Q ' is in phase with I Q , V 2 can be reduced.
  • the line voltage V 2 can be adjusted depending on how the reactive power is injected into the system.
  • Fig.1b demonstrates the basic concept of shunt reactive power compensation that can be used to stabilise the voltage in a power line. Shunt compensation is also known as parallel compensation because the reactive power source is placed in parallel with the load.
  • Reactive power compensation can also be done in a series manner. If an auxiliary or compensating voltage source V comp with its voltage vector being perpendicular to the current I is created and is placed in series with the load as shown in Fig.2 , the vector diagram shows that the output V 2 can be controlled. It should be noted that V comp can be 90° (assisting) or 270° (opposing) out of phase with I. This means V 2 can be increased or decreased to V 2 ' as shown in Fig.2 .
  • the scheme in Fig.2 is known as series reactive power compensation because the reactive power source is placed in series with the load.
  • the series and shunt reactive power compensators can be used individually or together.
  • a unified power flow controller (UPFC) is formed when a series and a shunt reactive power controller are used together as shown in Fig.3 .
  • the two reactive power controllers share a common dc power supply created by the capacitor.
  • the anti-parallel diodes of the two inverters form two natural diode rectifiers that connect the ac power line voltages to the dc capacitor. Consequently, the capacitor can be charged up and used as a dc voltage source.
  • the switching actions of the two inverters can be sinusoidally pulsed-width modulated so that their filtered PWM voltage waveforms are sinusoidal ( Fig.4 ).
  • the magnitude of the output voltage can be controlled by the modulation index and the phase can also be controlled with respect to the current.
  • the reactive power of the series and shunt compensators is injected through the isolation transformers into the power lines.
  • the reactive power controller can be practically realized with the use of a power inverter and an energy storage element, which can be either a large capacitor acting as a voltage source or an inductor acting as a current source as shown in Fig.5 .
  • the inverters are not restricted to two-level inverters shown in Fig.3 , Fig.4 and Fig.5 .
  • Multi-level inverters can in principle be used to generate the ac voltage waveforms. If multi-level inverters are used, the filtering efforts can be reduced at the expense of increased numbers of switches and circuit and control complexity.
  • reactive power controllers can be used to absorb or deliver reactive power.
  • reactive power compensators are used for medium to high power applications from hundreds of kilo-Volt-Amperes (kVA) to thousands of kVA.
  • kVA kilo-Volt-Amperes
  • UPFCs high power transmission lines.
  • UPFCs heavy-current applications such as welding facilities, which draw large and non-linear currents that deteriorate the power quality of the power source.
  • auxiliary voltage Va using a "series" reactive power controller (shown in the dotted box) in Fig.6 so that the output voltage of the controller Vo can be adjusted from the mains voltage Vs (typically 220V to 240V) down to a minimum voltage of 180V, which is the guaranteed minimum voltage for normal lighting system operation suggested by the manufacturers.
  • the dimming level (or the value of the output voltage) is set by a dimming command signal as shown in Fig.6 and is kept constant at the controlled voltage level so as to keep the light intensity of the lighting system stable.
  • patent GB2418786 also suggests the use of an extra shunt reactive power controller as a power factor correction circuit.
  • This concept is a modified use of the UPFC in Fig.3 , but its application is for the function of dimming (using a series reactive power controller) and power factor correction (using a shunt reactive power controller).
  • the circuit proposed in Fig.7 is not intended to be used for power stability as a UPFC is used for very high power systems.
  • the reactive power controllers in patents GB2405540.B and GB2418786 are used to reduce the output voltage Vo, which has to be less than or equal to the input mains voltage Vs.
  • known reactive power controllers are concerned with controlling the output voltage, or Vo as referred to above, of the reactive power controller which is being supplied to the load.
  • the controlled variable is the output voltage (or Vo as referred to above) of the series reactive power controller.
  • the present invention provides a power control circuit connectable to a load adapted to receive a power supply, the power control circuit adapted to absorb power from the power supply and adapted to deliver power to the power supply to stabilize at least one electrical parameter of the power supply.
  • the power absorbed and delivered by the power control circuit includes reactive power, or active power, or both.
  • the at least one electrical parameter is voltage, the power control circuit maintaining the power supply at a nominal supply voltage.
  • the load has a load voltage and the power control circuit provides an auxiliary voltage such that the vectorial sum of the load and auxiliary voltages equal the nominal supply voltage.
  • the load has a load current and the auxiliary voltage is at a phase angle perpendicular to the load current.
  • the power control circuit is further adapted to deliver power to the load to stabilize the at least one electrical parameter of the power supply.
  • the at least one electrical parameter is frequency, the power control circuit maintaining the power supply at a nominal supply frequency.
  • the load has a load voltage and the power control circuit decreases the load voltage when the frequency of the power supply is lower than the nominal supply frequency.
  • the load has a load voltage and the power control circuit increases the load voltage when the frequency of the power supply is higher than the nominal supply frequency.
  • the load voltage is preferably increased to exceed a nominal supply voltage.
  • the load has a load voltage and the power control circuit provides an auxiliary voltage to increase or decrease the load voltage.
  • the power control circuit includes a power controller for absorbing and delivering power thereby enabling the power control circuit to absorb and deliver power.
  • the power controller absorbs and delivers reactive power, or active power, or both.
  • the power controller is a reactive power controller.
  • the power controller is connected in series with the power supply and the load.
  • the power controller is connected in parallel across the load.
  • the power control circuit includes a second power controller, wherein the first power controller is connected in series with the power supply and the load, and the second power controller is connected in parallel across the first power controller and the load.
  • the first and second power controllers are interconnected through a power transfer connection.
  • the power transfer connection includes an energy storage element.
  • the energy storage element is preferably a capacitor connected in parallel across both the first and second power controllers.
  • either or both the first and second power controllers absorb and deliver power to the other of the first and second power controllers through the power transfer connection, and the other of the first and second power controllers absorbs and delivers power to the power supply or to the load.
  • the first power controller absorbs and delivers active power to the second power controller through the power transfer connection, and the second power controller absorbs and delivers active power to the power supply. Also preferably, the second power controller absorbs and delivers power to the first power controller through the power transfer connection, and the first power controller absorbs and delivers power to the load.
  • the power control circuit includes a second power controller, wherein the first power controller is connected in series with the power supply and the load, and the second power controller is connected in parallel across the load.
  • the power controller includes a power inverter and an energy storage element.
  • the energy storage element is a capacitor or an inductor.
  • the power inverter is a two-level power inverter or a multi-level power inverter. Also preferably, the power inverter is a pulse-width modulation power inverter.
  • the power control circuit includes a voltage controller for detecting the voltage of the power supply and providing a voltage control signal based on whether the voltage of the power supply is above or below a nominal supply voltage, the power control circuit referring to the voltage control signal to absorb or deliver power when the voltage of the power supply is above or below the nominal supply voltage, thereby maintaining the power supply at the nominal supply voltage.
  • the power control circuit includes an energy storage element and a second voltage controller, the second voltage controller for detecting a storage voltage across the energy storage element, receiving the voltage control signal provided by the first voltage controller, and providing a second voltage control signal, the power control circuit referring to the second voltage control signal to absorb or deliver power when the voltage of the power supply is above or below the nominal supply voltage, thereby maintaining the power supply at the nominal supply voltage.
  • the voltage controller is a proportional-integral controller or a lead-lag compensator.
  • the voltage control signal is provided to a power controller for absorbing and delivering power thereby enabling the power control circuit to absorb and deliver power.
  • the voltage controller forms part of the power controller.
  • the load has a load voltage
  • the power control circuit includes a synchronization network for detecting a phase angle of the power supply and providing a synchronization signal, the power control circuit referring to the synchronization signal to provide an auxiliary voltage at an appropriate phase angle such that the vectorial sum of the load and auxiliary voltages equal a nominal supply voltage, thereby maintaining the power supply at the nominal supply voltage.
  • the synchronization signal is provided to a power controller for absorbing and delivering power to enable the power control circuit to provide the auxiliary voltage at the appropriate phase angle.
  • the synchronization network forms part of the power controller.
  • the power control circuit includes a frequency controller for detecting the frequency of the power supply and providing a frequency control signal based on whether the frequency of the power supply is above or below a nominal supply frequency, the power control circuit referring to the frequency control signal to absorb or deliver power when the frequency of the power supply is above or below the nominal supply frequency, thereby maintaining the power supply at the nominal supply frequency.
  • the frequency control signal is provided to a power controller for absorbing and delivering power thereby enabling the power control circuit to absorb and deliver power.
  • the frequency controller forms part of the power controller.
  • the load is a non-critical load.
  • the load is a hot water heater or a lighting load.
  • the power control circuit is provided integrally with the load.
  • the power control circuit includes a bypass circuit having a bypass switch operable to connect the power supply directly to the load through the bypass circuit.
  • the power supply has a dynamically changing power profile and the power of the load follows the dynamically changing power profile.
  • the power supply is generated by one or more dynamically changing renewable energy sources.
  • the present invention provides a method of stabilizing at least one electrical parameter of a power supply connectable to a load, the method including absorbing power from the power supply or delivering power to the power supply.
  • the power being absorbed and being delivered includes reactive power, or active power, or both.
  • the at least one electrical parameter is voltage
  • the method includes maintaining the power supply at a nominal supply voltage.
  • the load has a load voltage and the method includes providing an auxiliary voltage such that the vectorial sum of the load and auxiliary voltages equal the nominal supply voltage.
  • the load has a load current and the auxiliary voltage is provided at a phase angle perpendicular to the load current.
  • the method includes delivering power to the load to stabilize the at least one electrical parameter of the power supply.
  • the at least one electrical parameter is frequency
  • the method includes maintaining the power supply at a nominal supply frequency.
  • the load has a load voltage and the method includes decreasing the load voltage when the frequency of the power supply is lower than the nominal supply frequency.
  • the load has a load voltage and the method includes increasing the load voltage when the frequency of the power supply is higher than the nominal supply frequency.
  • the load voltage is preferably increased to exceed a nominal supply voltage.
  • the load has a load voltage and the method includes providing an auxiliary voltage to increase or decrease the load voltage.
  • the method includes providing a power controller for absorbing and delivering power.
  • the power controller is connected in series with in series with the power supply and the load.
  • the power controller is connected in parallel across the load.
  • the method includes providing a second power controller, wherein the first power controller is connected in series with the power supply and the load, and the second power controller is connected in parallel across the first power controller and the load.
  • the method includes providing a second power controller, wherein the first power controller is connected in series with the power supply and the load, and the second power controller is connected in parallel across the load.
  • the method includes providing a voltage controller for detecting the voltage of the power supply and providing a voltage control signal based on whether the voltage of the power supply is above or below a nominal supply voltage, referring to the voltage control signal to absorb or deliver power when the voltage of the power supply is above or below the nominal supply voltage, thereby maintaining the power supply at the nominal supply voltage.
  • the load has a load voltage
  • the method includes providing a synchronization network for detecting a phase angle of the power supply and providing a synchronization signal, referring to the synchronization signal to provide an auxiliary voltage at an appropriate phase angle such that the vectorial sum of the load and auxiliary voltages equal a nominal supply voltage, thereby maintaining the power supply at the nominal supply voltage.
  • the method includes providing a frequency controller for detecting the frequency of the power supply and providing a frequency control signal based on whether the frequency of the power supply is above or below a nominal supply frequency, referring to the frequency control signal to absorb or deliver power when the frequency of the power supply is above or below the nominal supply frequency, thereby maintaining the power supply at the nominal supply frequency.
  • the method includes providing a power control circuit for absorbing and delivering power.
  • the power control circuit is provided integrally with the load.
  • the power supply has a dynamically changing power profile and power is absorbed from the power supply or delivered to the power supply such that the power of the load follows the dynamically changing power profile.
  • a power control circuit 1 connectable to a load 2 adapted to receive a power supply 3.
  • the power control circuit 1 is adapted to absorb power from the power supply 3 and adapted to deliver power to the power supply 3 to stabilize at least one electrical parameter of the power supply 3.
  • the power absorbed and delivered by the power control circuit 1 includes reactive power, or active power, or both.
  • the power control circuit 1 is further adapted to deliver power to the load 2 to stabilize the at least one electrical parameter of the power supply 3.
  • the at least one electrical parameter is voltage, with the power control circuit 1 maintaining the power supply 3 at a nominal supply voltage Vs.
  • This nominal supply voltage can be any of the nominal mains voltages provided by power grids in various countries.
  • the nominal supply voltage can be 110V, 220V, 230V, or 240V.
  • the load 2 has a load voltage Vo and the power control circuit 1 provides an auxiliary voltage Va such that the vectorial sum of the load and auxiliary voltages equal the nominal supply voltage Vs.
  • the load 2 has a load current Io and the auxiliary voltage Va is at a phase angle perpendicular to the load current Io.
  • the at least one electrical parameter is frequency, with the power control circuit 1 maintaining the power supply 3 at a nominal supply frequency.
  • This nominal supply frequency can be any of the nominal mains frequencies provided by power grids in various countries.
  • the nominal supply frequency can be 50Hz or 60Hz.
  • the load 2 has a load voltage Vo and the power control circuit 1 can decrease the load voltage when the frequency of the power supply is lower than the nominal supply frequency.
  • the power control circuit 1 can also increase the load voltage Vo when the frequency of the power supply is higher than the nominal supply frequency.
  • the load voltage Vo is increased to exceed a nominal supply voltage Vs. This can be done by having the power control circuit 1 provide an auxiliary voltage Va to increase or decrease the load voltage Vo.
  • the power control circuit 1 stabilizes both the electrical parameters of voltage and frequency of the power supply 3, with the power control circuit 1 maintaining the power supply 3 at a nominal supply voltage Vs, and maintaining the power supply 3 at a nominal supply frequency, as described above.
  • the power control circuit 1 includes a power controller 4 for absorbing and delivering power thereby enabling the power control circuit 1 to absorb and deliver power.
  • the power controller 4 can absorb and deliver reactive power, or active power, or both.
  • the power controller 4 is a reactive power controller.
  • the present invention proposes the methodology of using (1) the reactive power of the reactive power controller and/or (2) the active power control of the loads as a new generation of "smart loads" that serve the dual purposes of maintaining power grid stability and controlling the power consumptions of the loads.
  • the proposed smart load methodology involves both (1) the control of reactive power of the reactive power controller and (2) control of the active power consumption of the loads.
  • the reactive power controller 4 can be designed as a separate unit to the load 2 or it can be designed with the load in an integrated manner. It can be used for both electric loads with variable power consumption and also for loads with constant power, depending on the configurations of the reactive power controllers.
  • smart loads based on embodiments of the present invention can be installed all over smart grids and provide stabilising effects (or cushioning effects) to power lines over the smart grids.
  • the proposed methodology of the invention can be adopted in domestic water heaters and road lighting systems, which are distributed all over cities by the nature of their mode of installation.
  • a reactive power controller can absorb and deliver reactive energy so it can effectively vary (decrease and increase) the power line voltage.
  • a reactive power controller can absorb and deliver reactive energy so it can effectively vary (decrease and increase) the power line voltage.
  • a reactive power controller 4 is proposed to be used as an "electric spring” or “voltage stabiliser” to keep stable the voltage of the power lines to which this reactive power controller is connected.
  • the ability of the reactive power controller to absorb and deliver reactive power can be used to maintain voltage stability. Since the reactive power controllers are connected with the electric loads to form “smart loads", which are distributed for example over cities or other power grids, the installations of the proposed smart loads will provide many local “electric springs” or “voltage stabilisers” distributed all over the cities or the power grids to form “smart grids”. They can therefore provide voltage stabilisation and damping of oscillations over the power grids.
  • Such distributed voltage support over a large power network of smart grids is similar to the distributed mechanical support provided by the springs of a mattress as shown in Fig.9 .
  • the control loop of the reactive power controller will be much different from that used in GB2405540.B and GB2418786 , which are proposed not for power grid voltage stabilization, but for the dimming of lighting systems only.
  • the smart load with the series reactive power controller structure is now explained with the aid of Fig.11 .
  • the loads here could be any electric loads that do not require constant power.
  • Application examples are domestic and industrial water heaters, individual lighting system or preferably a network of lighting systems for public areas, and some electrical appliances that can tolerate a wider fluctuation of supply voltage that exceeds the nominal tolerance. These are also known as "non-critical" loads.
  • Fig.11a shows the schematic of a series-type smart load control method (i.e. Structure-1 of Fig.10 ). Unlike the use of reactive power controllers for dimming purposes which sets a load voltage reference Vo_ref for controlling the load voltage Vo, the new control method of embodiments of the present invention uses the nominal mains voltage, also called the nominal supply voltage, Vs_ref as a reference. For example, for countries that use a nominal supply voltage of 230V as phase voltage, the voltage reference of this control method Vs_ref could be set in the electronic control board of the control system as equivalent to 230V. This voltage reference representing 230V is implemented as a constant voltage in the control board of a power controller in accordance with an embodiment of the present invention.
  • the switch S is a bypass switch, which when closed, allows power to bypass the series reactive power controller and connects the load directly to the power lines without reactive power control.
  • Fig.11b shows a similar schematic which includes a network of loads, instead of a single load.
  • the difference between the actual ac mains voltage Vs and the reference mains voltage is fed to a voltage controller 5, which can be any suitable controller such as a proportional-integral (PI) controller or a lead-lag compensator.
  • the output of the voltage controller 5 provides a control signal for the Pulse-Width-Modulated (PWM) Generator 6.
  • a synchronization network 7 is used to provide the phase information for the PWM Generator 6, which generates the switching signals for the power semiconductor switches of a power inverter 8 to generate a high-voltage sinusoidal PWM voltage waveform.
  • the dc voltage of the power inverter 8 is usually obtained from a capacitor 9 which is charged through the anti-parallel diodes of the inverter switches (like a diode rectifier with an output dc capacitor).
  • the PWM voltage generated by the power inverter 8 is filtered by a low-pass LC filter so that an auxiliary sinusoidal voltage Va can be created.
  • the power inverter 8 (being used as part of a reactive power controller) will not consume active power in the process of creating the auxiliary voltage Va, assuming that the conduction loss, core loss and the switching loss of the power inverter circuit and filter are negligible.
  • auxiliary voltage Va can be generated in either polarity, so that the series reactive power controller will cause the actual power line voltage Vs to follow its nominal reference value Vs_ref
  • the schematic proposed in Fig.11 can be considered as an "electric spring” or “voltage stabiliser” as shown in Fig.12 .
  • FIG.11c An alternative control method for fast response of the series structure is shown in Fig.11c .
  • the novel feature of having a series reactive power controller connected in series with the load, with the combined unit connected to the power lines remains the same as Figs.11a and 11b .
  • this method includes a fast inner control loop based on the sensing of the dc voltage across the storage capacitor 9. Since the magnitude of the voltage Va generated by the PWM inverter 8 depends on the dc voltage Vdc, any variation of Vdc is a faster indication of the load demand response than the indication obtained from the variation of the rms value of Vs.
  • Figs.11a , 11b and 11c can be incorporated into shunt reactive power control to form an electric spring either (i) as an independent unit for turning an existing load into a smart load or (ii) as an integrated part of the load to form an integrated smart load.
  • the setup consists of two sets of loads.
  • the load network 2 connected in series to the series reactive power controller 4 is together called the "smart load network".
  • These loads 10 represent other loads that are not under the control of embodiments of the present invention in the same power grid.
  • the smart load network in the test includes resistors (representing water heaters) and some ballast driven light-emitting diode LED devices (representing road lighting systems).
  • the first series of tests involve the generation of an unstable mains, or supply, voltage with a sinusoidal fluctuation. Due to this dynamically changing nature, the power flow is not constant and there are obvious fluctuations in the power line voltage as recorded in Figs.14a-f .
  • the measurements were captured initially with the "electric spring” (i.e. the series reactive power controller) turned off and the bypass switch S closed. Measurements were then captured with the “electric spring” (i.e. the reactive power controller 4) activated and the bypass switch S open.
  • the rms voltage values of the power lines (Vs), the voltage across the smart load network and the voltage of the electric spring (Va) are plotted in Fig.16a .
  • the setup is designed to generate the same unstable voltage patterns in the mains twice by the simulated wind energy source.
  • the bypass switch S is closed and the electric spring is deactivated.
  • the voltage of the smart load network is therefore the same as the mains voltage which fluctuates below the nominal value of 220V in this test.
  • the second half of the test the same unstable voltage from the simulated wind energy source is generated. It should be noted that there some points in the programmed voltage pattern where the generated mains voltage reaches or exceeds 220V in Fig.16a .
  • Fig.16a it can be seen from the first half when the electric spring is turned off (i.e. bypass switch S is closed) that the voltage of the smart load network follows the unstable mains voltage pattern.
  • the bypass switch S is opened and the electric spring is turned on in the second half with the same unstable voltage pattern from the wind energy source, the auxiliary voltage generated by the electric spring varies in such a dynamical manner that the mains voltage of the power lines is restored closely to the preset nominal value of 220V.
  • the mains voltage vector of Vs is equal to the vectorial sum of voltage across the power controller 4, Va, and the voltage across the load 2, Vo. These are related in vectorial form as shown in Fig.17 .
  • Their values in Fig.16a are scalar values. It is important to note that when the generated mains voltage reaches or exceeds 220V, the voltage of the electric spring drops to zero. This measurement confirms the dynamic functions of the electric spring in providing reactive power compensation to maintain voltage regulation dynamically.
  • Structure-1 illustrates the unique feature that using a series reactive power controller in series with an electric load can turn the combined unit into a smart load which can (1) provide reactive power compensation for mains power supply voltage regulation and (2) enable the load demand to follow a dynamic power (e.g. renewable or wind power) profile.
  • a series reactive power controller in series with an electric load can turn the combined unit into a smart load which can (1) provide reactive power compensation for mains power supply voltage regulation and (2) enable the load demand to follow a dynamic power (e.g. renewable or wind power) profile.
  • the shunt-type structure in Fig.10b will be more appropriate because the operation of the shunt reactive power controller serves to maintain good voltage regulation for the load without substantially affecting the active power consumption of the load.
  • Fig.17 shows the vector diagram of Vs, Va and Vo.
  • the load is a resistive one (R1) such as a water heater
  • V o 2 V s 2 ⁇ V a 2
  • P 1 / R 1 V o 2
  • Equation (3) now provides the mathematical relationship between power generated and power consumed.
  • the first term on the right hand side of (3) is the power consumed by the non-critical load and the second term is the power consumed by other loads.
  • Vs in (3) is a constant.
  • a reduction in wind power generation Pin leads to an increase of Va, and vice versa.
  • An increase in Va, according to (1) results in a reduction in Vo, and therefore will decrease the load power according to (2). Therefore, these three equations provide the explanation for why the load demand will follow the wind power based on the proposed method.
  • Fig.22 further illustrates this point while comparing the power profiles of non-critical and critical loads.
  • series and shunt arrangements can be combined to form the series-shunt arrangements as shown in Fig.10c and Fig.10d .
  • Structure-3 of Fig.10c can be realized in the form as shown in Fig.18 . It should be noted that Structure-3 retains the novel feature that a series power controller 4 is connected in series, as a first power controller, with the load 2 and the combined unit is connected to the power lines 3.
  • the power control circuit 1 of Structure-3 further includes a second power controller 4' connected in parallel across the series, or first, power controller 4 and the load 2.
  • the second power controller 4' is also called a shunt power controller.
  • Structure-3 offers other control function possibilities if the two power controllers are allowed to handle both active and reactive power. With the provision of a power transfer connection 11 between the shunt power controller 4' and the series power controller 4 (e.g.
  • the power transfer connection 11 in the present embodiment is a shared capacitor storage element as shown in the circuits in Figs.18 , 19 and 20 . More particularly, the capacitor is connected in parallel across both the first and second power controllers 4 and 4'.
  • An example of this operation is to use the series power controller 4 to absorb active power, which is then transferred back to the power line 3 by the shunt power controller 4' in order to avoid necessary power loss.
  • the voltage vector of Va can be at any angle with respect with the current vector Io. In this way, the voltage vector of the mains voltage Vs can be changed with a smaller voltage vector of Va (when compared with Fig.17 ), allowing the voltage rating of the series controller 4 to be reduced.
  • the adjustment of Vo means that the active power of the smart load can be controlled in this operating mode.
  • Structure-4 shown in Fig.10d suggests a means to boost the load voltage under control.
  • the power control circuit 1 includes a second power controller 4', wherein the first power controller 4 is connected in series with the power supply 3 and the load 2, and the second power controller 4' (also known as a shunt power controller) is connected in parallel across the load 2.
  • the series reactive power controller 4 is controlled in inductive mode and is simulated as an equivalent inductor with a series resistance.
  • the shunt reactive power controller 4' is operated in capacitive mode and is thus represented as an equivalent capacitor with a small resistance. It will be appreciated that the power line voltage can be slightly boosted if necessary.
  • the smart load methodology with reactive power control capability essentially includes (1) reactive power compensation functions for voltage stability and (2) load power control.
  • the demand response (load power) can now follow the power generation and play a supporting role in maintaining power line voltage stability, which is a unique feature required in future smart grids.
  • the priority should and can be placed on security of the power grids. This means that loads may have to vary in order to maintain power grid stability.
  • the smart load as provided by embodiments of the present invention, should react with the priority of maintaining voltage stability.
  • Fig.22 illustrates the difference in power profiles between non-critical loads and critical loads, where the non-critical loads are controlled by power control circuits or power controllers of the present invention.
  • the power of non-critical loads as controlled by power control circuits or power controllers of the present invention follows the dynamically changing power profile of the dynamically changing power supply, such as those based on renewable energy sources.
  • some embodiments of the present invention are adapted to stabilize the frequency of the power supply.
  • the frequency of the generators may deviate from the nominal values of 50Hz or 60Hz depending on the load demand. If the load demand exceeds the power generated, the frequency will be reduced slightly from the nominal value, and vice versa. Consequently, frequency instability might occur. This is shown schematically in Fig.23 .
  • Structrue-3 as described above, can be used to improve the frequency instability problem by controlling the real power of the non-critical load 2 as illustrated in Fig.24 .
  • a reliable frequency feedback is compared with a reference frequency (of the nominal mains frequency 50Hz or 60Hz).
  • the frequency error can be fed to a frequency controller 12 which in turn control the first power controller 4 and the second power controller 4' such that:
  • a method of stabilizing at least one electrical parameter of a power supply connectable to a load including absorbing power from the power supply or delivering power to the power supply.
  • the power supply is the power supply 3 described above and the load is the load 2 described above.
  • the embodiment includes providing the power control circuit 1, including providing the power controller 4 or the power controllers 4 and 4', as described above, for absorbing and delivering power.
  • Other embodiments include method steps that have been previously described above or that will be easily appreciated from the above description.
  • smart grids In summary, in emerging smart grid power systems (“smart grids”), it is expected that renewable energy sources (such as wind farms and solar photovoltaic plants) with dynamically changing power flow will be installed. Future smart grids will be different from existing power grids in which the power generation is well-controlled by the power stations. The foreseeable massive penetration of renewable energy sources that are often distributed in the power grids would likely cause power system instabilities (such as instability and oscillations in voltage and frequency).
  • Particular embodiments of the present invention are related to the use of distributed reactive power controllers designed with or integrated with electric loads for improving the system voltage and frequency stability of smart power grid systems (smart grids), particularly those smart grids that have a significant portion of power coming from dynamically changing renewable energy sources such as wind and solar photovoltaic power plants.
  • smart grid systems smart grids
  • Embodiments of the present invention include configurations that can be associated to electric loads with fairly high tolerance with wide variations in ac supply voltage such as lighting systems and heating systems, and also electric loads that require tight voltage regulations.
  • the proposed smart electronic load of some embodiments of the invention has a reactive power controller connected in series with the loads.
  • Embodiments of the present invention include a basic unit that consists of a reactive power controller being in series with a load. This basic unit (i.e. a series reactive power controller and the load) will then be connected across the power lines. This basic unit is different from the convention use of a static VAR compensator which is connected across the power lines. Shunt reactive power controllers can be added to this basic structure.
  • known reactive power controllers are concerned with controlling the output voltage, or Vo as referred to above, of the reactive power controller which is being supplied to the load.
  • the controlled variable is the output voltage (or Vo as referred to above) of the series reactive power controller.
  • Embodiments of the present invention abandon this traditional output voltage feedback and control methodology. More particularly, embodiments of the present invention control the input voltage (Vs) of the series reactive power controller, which is connected in series with a load.
  • the output voltage (Vo) of the series reactive power controllet is allowed to fluctuate dynamically according to the renewable power generation profile.
  • This series reactive power controller (with input voltage Vs feedback and control) and the series-connected load will form a new smart load unit for power system stability control.
  • the proposed smart loads are expected to be distributed over smart grids and continue to operate at modified power levels under normal situations.
  • a power control circuit connectable to a load adapted to receive a power supply
  • the power control circuit adapted to absorb power from the power supply and adapted to deliver power to the power supply to stabilize at least one electrical parameter of the power supply.
  • the power absorbed and delivered by the power control circuit includes reactive power, or active power, or both.
  • the at least one electrical parameter is voltage, the power control circuit maintaining the power supply at a nominal supply voltage.
  • the load has a load voltage and the power control circuit provides an auxiliary voltage such that the vectorial sum of the load and auxiliary voltages equal the nominal supply voltage.
  • the load has a load current and the auxiliary voltage is at a phase angle perpendicular to the load current.
  • the power control circuit is further adapted to deliver power to the load to stabilize the at least one electrical parameter of the power supply.
  • the at least one electrical parameter is frequency, the power control circuit maintaining the power supply at a nominal supply frequency.
  • the load has a load voltage and the power control circuit decreases the load voltage when the frequency of the power supply is lower than the nominal supply frequency.
  • the load has a load voltage and the power control circuit increases the load voltage when the frequency of the power supply is higher than the nominal supply frequency.
  • the load voltage is increased to exceed a nominal supply voltage.
  • the load has a load voltage and the power control circuit provides an auxiliary voltage to increase or decrease the load voltage.
  • the power control circuit includes a power controller for absorbing and delivering power thereby enabling the power control circuit to absorb and deliver power.
  • the power controller absorbs and delivers reactive power, or active power, or both.
  • the power controller is a reactive power controller.
  • the power controller is connected in series with the power supply and the load.
  • the power controller is connected in parallel across the load.
  • the power control circuit includes a second power controller, and wherein the first power controller is connected in series with the power supply and the load, and the second power controller is connected in parallel across the first power controller and the load.
  • the first and second power controllers are interconnected through a power transfer connection.
  • the power transfer connection includes an energy storage element.
  • the energy storage element is a capacitor connected in parallel across both the first and second power controllers.
  • either or both the first and second power controllers absorb and deliver power to the other of the first and second power controllers through the power transfer connection, and the other of the first and second power controllers absorbs and delivers power to the power supply or to the load.
  • the first power controller absorbs and delivers active power to the second power controller through the power transfer and the second power controller absorbs and delivers active power to the power supply.
  • the second power controller absorbs and delivers power to the first power controller through the power transfer connection, and the first power controller absorbs and delivers power to the load.
  • the power control circuit includes a second power controller, and wherein the first power controller is connected in series with the power supply and the load, and the second power controller is connected in parallel across the load.
  • the power controller includes a power inverter and an energy storage element.
  • the energy storage element is a capacitor or an inductor.
  • the power inverter is a two-level power inverter or a multi-level power inverter.
  • the power inverter is a pulse-width modulation power inverter.
  • the power control circuit includes a voltage controller for detecting the voltage of the power supply and providing a voltage control signal based on whether the voltage of the power supply is above or below a nominal supply voltage, the power control circuit referring to the voltage control signal to absorb or deliver power when the voltage of the power supply is above or below the nominal supply voltage, thereby maintaining the power supply at the nominal supply voltage.
  • the power control circuit includes an energy storage element and a second voltage controller, the second voltage controller for detecting a storage voltage across the energy storage element, receiving the voltage control signal provided by the first voltage controller, and providing a second voltage control signal, the power control circuit referring to the second voltage control signal to absorb or deliver power when the voltage of the power supply is above or below the nominal supply voltage, thereby maintaining the power supply at the nominal supply voltage.
  • the voltage controller is a proportional-integral controller or a lead-lag compensator.
  • the voltage control signal is provided to a power controller for absorbing and delivering power thereby enabling the power control circuit to absorb and deliver power.
  • the voltage controller forms part of the power controller.
  • the load has a load voltage
  • the power control circuit includes a synchronization network for detecting a phase angle of the power supply and providing a synchronization signal, the power control circuit referring to the synchronization signal to provide an auxiliary voltage at an appropriate phase angle such that the vectorial sum of the load and auxiliary voltages equal a nominal supply voltage, thereby maintaining the power supply at the nominal supply voltage.
  • the synchronization signal is provided to a power controller for absorbing and delivering power to enable the power control circuit to provide the auxiliary voltage at the appropriate phase angle.
  • the synchronization network forms part of the power controller.
  • the power control circuit includes a frequency controller for detecting the frequency of the power supply and providing a frequency control signal based on whether the frequency of the power supply is above or below a nominal supply frequency, the power control circuit referring to the frequency control signal to absorb or deliver power when the frequency of the power supply is above or below the nominal supply frequency, thereby maintaining the power supply at the nominal supply frequency.
  • the frequency control signal is provided to a power controller for absorbing and delivering power thereby enabling the power control circuit to absorb and deliver power.
  • the frequency controller forms part of the power controller.
  • the load is a non-critical load.
  • the load is a hot water heater - lighting load.
  • the power control circuit is provided integrally with the load.
  • the power control circuit includes a bypass circuit having a bypass switch operable to connect the power supply directly to the load through the bypass circuit.
  • the power supply has a dynamically changing power profile and the power of the load follows the dynamically changing power profile.
  • the power supply is generated by one or more dynamically changing renewable energy sources.
  • a method of stabilizing at least one electrical parameter of a power supply connectable to a load including absorbing power from the power supply or delivering power to the power supply.
  • the power being absorbed and being delivered includes reactive power, or active power, or both.
  • the at least one electrical parameter is voltage
  • the method includes maintaining the power supply at a nominal supply voltage
  • the load has a load voltage and the method includes providing an auxiliary voltage such that the vectorial sum of the load and auxiliary voltages equal the nominal supply voltage.
  • the load has a load current and the auxiliary voltage is provided at a phase angle perpendicular to the load current.
  • the method further includes delivering power to the load to stabilize the at least one electrical parameter of the power supply.
  • the at least one electrical parameter is frequency
  • the method includes maintaining the power supply at a nominal supply frequency
  • the load has a load voltage and the method includes decreasing the load voltage when the frequency of the power supply is lower than the nominal supply frequency.
  • the load has a load voltage and the method includes increasing the load voltage when the frequency of the power supply is higher than the nominal supply frequency.
  • the load voltage is increased to exceed a nominal supply voltage.
  • the load has a load voltage and the method includes providing an auxiliary voltage to increase or decrease the load voltage.
  • the method including providing a power controller for absorbing and delivering power.
  • the power controller is connected in series with in series with the power supply and the load.
  • the power controller is connected in parallel across the load.
  • the method includes providing a second power controller, wherein the first power controller is connected in series with the power supply and the load, and the second power controller is connected in parallel across the first power controller and the load.
  • the method includes providing a second power controller, wherein the first power controller is connected in series with the power supply and the load, and the second power controller is connected in parallel across the load.
  • the method includes providing a voltage controller for detecting the voltage of the power supply and providing a voltage control signal based on whether the voltage of the power supply is above or below a nominal supply voltage, referring to the voltage control signal to absorb or deliver power when the voltage of the power supply is above or below the nominal supply voltage, thereby maintaining the power supply at the nominal supply voltage.
  • the load has a load voltage
  • the method includes providing a synchronization network for detecting a phase angle of the power supply and providing a synchronization signal, referring to the synchronization signal to provide an auxiliary voltage at an appropriate phase angle such that the vectorial sum of the load and auxiliary voltages equal a nominal supply voltage, thereby maintaining the power supply at the nominal supply voltage.
  • the method includes providing a frequency controller for detecting the frequency of the power supply and providing a frequency control signal based on whether the frequency of the power supply is above or below a nominal supply frequency, referring to the frequency control signal to absorb or deliver power when the frequency of the power supply is above or below the nominal supply frequency, thereby maintaining the power supply at the nominal supply frequency.
  • the method includes providing a power control circuit for absorbing and delivering power.
  • the power control circuit is provided integrally with the load.
  • the power supply has a dynamically changing power profile and power is absorbed from the power supply or delivered to the power supply such that the power of the load follows the dynamically changing power profile.

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EP2625759A1 (fr) 2013-08-14
WO2012045231A1 (fr) 2012-04-12
EP2625759B1 (fr) 2019-08-14
US11705730B2 (en) 2023-07-18
EP2625759A4 (fr) 2014-09-24
US20170256944A1 (en) 2017-09-07

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